1. Field of the Invention
The present invention generally relates to an electromagnetically driven valve, and more particularly to an electromagnetically driven valve wherein a coil for lifting an intake/exhaust valve in a valve-opening direction and a coil for lifting the same in a valve-closing direction are constituted of an identical connection.
2. Description of the Background Art
As to a conventional electromagnetically driven valve, for example Japanese Patent Laying-Open No. 2002-115515 discloses an actuator for an electromagnetically driven valve having an object of facilitating mounting on a vehicle and to reduce weight and costs (Patent Document 1). The actuator for an electromagnetically driven valve disclosed in Patent Document 1 implements an intake valve and an exhaust valve of an engine. The actuator for an electromagnetically driven valve includes one electromagnet and two moving elements arranged above and below the electromagnet, respectively, to cause reciprocating motion of the valve element between a fully open position and a fully closed position. To the moving elements, elastic force of a plurality of springs is applied, whereby the valve element is biased to a neutral position, which is slightly shifted from an intermediate position between the fully open position and the fully closed position toward the opening direction or the closing direction.
Japanese Patent Laying-Open No. 05-018220 discloses an electromagnetically driven valve having an object of attaining sufficient driving force even when the stroke of the valve is long (Patent Document 2).
In the actuator for an electromagnetically driven valve disclosed in Patent Document 1, in an initial drive mode, one of the two moving elements is positioned so that it is nearer to the electromagnet than the other is. Accordingly, when the electromagnet is electrically supplied, a difference arises between electromagnetic force applied to one of the moving elements and that applied to the other, whereby the moving elements are drawn toward one end of the electromagnet.
However, since the difference between the electromagnetic forces respectively applied to the two moving elements is small, the driving force sufficient for moving the valve element to the fully open position or to the fully closed position cannot be attained. Therefore, in Patent Document 1, the electric supply is shut off so as to allow free oscillation of the moving elements using the stored energy of the springs. By repetition of intermittent electric supply, the amplitude of the moving elements is gradually increased, so that the valve element ultimately shifts to the fully open position or the fully closed position. In this case, it takes time until the moving elements are moved from the neutral position to the fully open position or the fully closed position.